1. Field of the Invention
The present invention generally relates to a bicycle rear derailleur. More specifically, the present invention relates to base member of a bicycle rear derailleur which is mounted on the frame of a bicycle.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle rear derailleur.
A bicycle rear derailleur is used to selectively engage a chain with one of a plurality of sprockets that rotate with the rear wheel of the bicycle. A typical rear derailleur comprises a base member, a movable member supporting a chain guide and a pair of links coupled between the base member and the movable member so that the chain guide moves laterally relative to the base member. The base member usually is mounted to the rear end of the bicycle frame by a mounting bolt that screws into a threaded opening formed in the rear end of the bicycle frame. The chain guide moves the chain in order to transfer the chain to one of the rear sprockets. The chain guide typically has an outside plate member, an inside plate member, a guide pulley rotatably mounted between the two plate members at first ends of the two plate members, and a tension pulley rotatably mounted between both plate members at the other ends of both plate members.
In use, one end of an operating cable is typically connected to one of the links, and another end of the operating cable is connected to a shift control device mounted on the bicycle handlebar. When the rider operates the shift control device, the operating cable is pulled or released accordingly. The operating cable pulls or releases the link, which causes the link to pivot relative to the base member and move the chain guide laterally to shift the bicycle chain from one rear sprocket to another rear sprocket.